JPH05268794A - Inverter and restarting method therefor after instantaneous power interruption - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to eliminate the need for a circuit using a voltage detection transformer or a photocoupler for a phase detector used in an inverter having an instantaneous power failure restart function, and to achieve a compact size. , To provide a low-price, high-reliability inverter device. [Constitution] In an inverter device having a converter 1, a smoothing capacitor 2, an inverter 3, and a current detector 4, when an instantaneous power failure occurs, the upper arm transistor Q of the inverter section
The ON signal PB is simultaneously sent only to R, QS, and QT, the direction of the short-circuit current that flows is detected by the current direction reversal detection circuit 12, the residual voltage frequency and phase are detected based on this signal, and the detected frequency and It is configured to be restarted based on the phase and the power recovery signal of the power failure detection circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device, and particularly when recovering from an instantaneous power failure, a voltage is applied in accordance with the phase of the residual voltage of an induction motor (IM) connected to the output, and a restart current is applied. The present invention relates to an inverter device having an instantaneous power failure restart function, which is configured to reduce the peak value of 1) as much as possible.

[0002]

2. Description of the Related Art FIG. 6 shows a circuit diagram of a conventional inverter device having a restart function for an instantaneous power failure. In FIG. 6, 1
Is a converter unit for rectifying AC to DC, and 2 is a smoothing capacitor C for smoothing DC rectified by this converter unit.
B, 3 is an inverter unit for converting DC into AC of arbitrary frequency, 4 is a current detector for detecting the output current of the inverter, 5 is an induction motor connected to the output of the inverter, 6
Is a phase detector, 9 is a power failure detection circuit, and 10 is an inverter control circuit. In the inverter device configured as described above, terminals R, S, and T are connected to a power supply, and AC power from the power supply is converted into AC power having an output frequency according to a frequency command (not shown) and connected to the output. It is supplied to the electric motor 5.

The following is a description of the conventional restart of an instantaneous power failure when an instantaneous power failure occurs in the power source when the inverter device operates the induction motor at a variable speed as described above. First, when a power failure occurs, the transistors QR, QS provided in the inverter section
The base currents of QT, QU, QV, and QW are all cut off, and the motor enters the free-run state. However, since the secondary current flowing through the rotor of the induction motor decreases in accordance with the electric time constant of the rotor itself, the residual magnetic flux usually remains for 0.1 to 1 second. Due to this residual magnetic flux, a residual voltage is generated on the primary side of the induction motor. Instantaneous power failure restart is an operation method in which the voltage is reapplied to the induction motor and restarted if the power is restored while the residual voltage is generated. If the phase is opposite to that, an excessive current flows by that amount, and there is a problem of an overcurrent trip. Therefore, conventionally, in order to detect the residual voltage of the induction motor, the phase detector 6 shown in FIG. 6 is provided at the output of the inverter device, and the inverter is controlled so as to have the same phase as the detected residual voltage. It was

The phase detector 6 separates the high-voltage part of the main circuit and the low-voltage part of the control circuit from each other.
T) or a circuit using the photocoupler (PHC) 7 shown in FIG. 7 has been used. The conventional voltage detecting transformer uses a voltage detecting transformer which is not usually used in a general-purpose inverter, and thus has a problem in cost and size reduction of the inverter device. Further, the phase detector 6 using the photocoupler (PHC) 7 needs to limit the current flowing through the photocoupler PHC to about 15 mA, so that if the effective voltage of the high voltage section is 220V,
The current limiting resistance (RUV) 8 is, for example, effective 3.3 W, 15
The capacity of kΩ is required, and it is 1 because of the reliability and the margin of heat capacity.
A resistor of about 0 W will be used. For this reason, the size of the resistor itself becomes large, and there is a problem in downsizing the inverter device in consideration of heat radiation and the like. The number of parts also increased and there was a problem in terms of reliability.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to use a voltage detecting transformer (PT) or a photocoupler (PHC) 7 for a phase detector used in an inverter having an instantaneous power failure restart function. The purpose of the present invention is to provide a compact, low-priced, highly reliable inverter device that does not require a circuit.

[0006]

According to the present invention, in order to solve the above-mentioned problems, a signal for simultaneously conducting the switching elements of the upper arm or the lower arm of an inverter when an instantaneous power failure occurs is generated by a short-circuit current when this signal is turned off. Is given at intervals such that decreases and becomes zero. The current flowing at this time is detected by a current detector, the direction of the detected current is discriminated, and the phase of the residual voltage is detected. Then, the voltage is reapplied according to the phase of the residual voltage.

[0007]

In a momentary power failure, the switching element of the inverter section is simultaneously supplied with a conduction signal to the upper arm or the lower arm, so that the terminals of the induction motor are short-circuited by the upper arm or the lower arm. At this time, current flows in the short circuit due to the residual voltage of the induction motor. Also, when the conduction signal is turned off, this current decreases to zero.

The current flowing at this time is detected by the current detector, and the direction of the detected current is determined. The phase of the residual voltage is detected according to the direction of the detected current, and the voltage is reapplied according to the phase of the residual voltage.

[0009]

EXAMPLE FIG. 1 shows an example of the present invention. In FIG. 1, the same parts as those in FIG. 6 are designated by the same reference numerals. Reference numeral 11 denotes a simultaneous conduction control signal generation command circuit for instructing simultaneous conduction of the upper arm or the lower arm of the inverter at a predetermined interval when the power failure detection circuit 9 detects a power failure. 12
Is a current direction reversal detection circuit that receives a signal from the current detector 4 and detects that the current direction is reversed. Reference numeral 13 is a restart timing generation circuit that detects the timing of reapplying the voltage after power recovery. Reference numeral 14 is an inverter control circuit. Reference numeral 15 is a current level detection circuit. Each of these circuits 9, 11, 12, 13, 14, and 15 can be configured as an independent circuit, but can also be configured in common by a circuit using a microcomputer.

In the inverter device configured as described above, when an instantaneous power failure occurs, the output of the inverter is cut off for self-protection after the lapse of the instantaneous power failure operation guarantee time. Since the output is cut off, as shown in FIG.
Normally, the residual voltage of the induction motor drops rapidly with time, with a time constant of 0.1 to 1 second, but the control power supply is slowly obtained because it is obtained by DC / DC conversion from both ends of the smoothing capacitor 2 (CB). To descend. The control circuit can operate until the voltage drops below the undervoltage detection level. Therefore, even during a momentary power failure, the control system can be controlled until the residual voltage of the induction motor disappears.

The present embodiment will be described under the above conditions.

FIG. 3 shows each operation when restarting after an instantaneous power failure. The area A indicates the normal driving operation before the instantaneous blackout. B
The area of indicates the guaranteed operation time for the momentary power failure. The area C indicates the period of the free-run state when the instantaneous blackout occurs. Area D indicates the preparation period for restarting after the power is restored. Area E indicates the period of restart acceleration. Area F indicates a normal operation period in which restart is completed.

Since the output is shut off after the momentary power failure operation continuation guarantee time, the residual voltage appears at the terminal from the point X and decays with time. In order to detect this residual voltage, in this embodiment, the base current is simultaneously passed through the upper arm transistors QR, QS and QT of the inverter section during the free run state, and the phase of the residual voltage of the induction motor is determined from the direction of the current flowing at this time. Is to seek.

When the power failure detection circuit 9 detects a power failure, the simultaneous conduction control signal generation command circuit 11 operates during the PB output period indicated by the signal d in FIG.
The inverter control circuit 14 is instructed to simultaneously supply the pulse base signal as indicated by PB to the transistors QR, QS, and QT at predetermined intervals.

FIG. 4 shows details of the residual voltage em of the induction motor, the base signal PB of the transistors QR, QS and QT, the output current i and the direction inversion detection signal a of the output current.

When the signal PB is applied to the bases of the transistors QR, QS and QT at the same time, a short circuit for short-circuiting the terminals of the induction motor is formed in the upper arm of the inverter. At this time, for example, looking at the U-phase and the V-phase, a short-circuit current flows in the current path (1) and the current path (2) as shown in FIG. The induction motor 5 determines whether the current path (1) or the current path (2) is set.
It depends on the polarity of the residual voltage. That is, if the V-phase terminal has a higher potential than the U-phase terminal, the current path (1) is established. Conversely, if the U-phase terminal has a higher potential than the V-phase terminal, the current path (2) is established. When the base signals of the transistors QR, QS, QT turn off, the transistors QR, QS, QT turn off, so the current path (1)
Alternatively, the short circuit current of the current path (2) is changed to the current path (3) or the current path (4). The smoothing capacitor 2 is included in the current paths (3) and (4), and the current changed to the current paths (3) and (4) due to the voltage of the smoothing capacitor 2 decreases. Assuming that the ON period of the base signal is T1 and the pulse period is T, this short-circuit current will definitely become zero in the OFF period because the voltage of the smoothing capacitor 2 is larger than the residual voltage if T1 / T is 0.5 or less. .. Therefore, when this current is detected by the current detector 4 (CT), a waveform as shown by the current waveform i in FIG. 4 is obtained. As can be seen from this waveform, the direction in which the short-circuit current flows matches the polarity of the residual voltage indicated by em. Therefore, by detecting this current direction, the polarity of the residual voltage can be known, and it can be seen that the point at which the direction of the current reverses is the zero-cross point of the residual voltage. The period T of the base signal PB should be as short as possible in order to reduce the deviation of the detection of the zero cross point of the residual voltage. However, when the cycle of the base signal PB becomes short, the peak value of the short-circuit current i becomes low and current detection becomes difficult. The current direction inversion detection circuit 12 shown in FIG. 1 is configured to store the current direction when the pulse PB is applied and output the signal shown in a of FIG. This can be configured by a sample hold circuit. However, the sample-hold circuit in this case does not need to hold the size, and may hold only the polarity. Alternatively, a control circuit using a microcontroller can be implemented by digitally storing it in a memory. The output signal b of the power failure detection circuit 9 and the output of the current direction reversal detection circuit 12 are input to the restart timing generation circuit 13, and the current direction reversal detection circuit 12 is detected after the power failure detection circuit 9 detects the power restoration. The timing at which the output of (1) is inverted (the timing of Y in FIG. 3) is detected and a signal is output to the inverter control circuit 14. This signal is shown as the c signal in FIG. The phase of the reapplied voltage is determined based on the polarities of the c signal and the output signal of the current direction inversion detection circuit 12.

Further, the rotation speed of the induction motor can be known by measuring the interval of the output reversal timing of the inverter control circuit 14. That is, N = 1 / (2τn · P) −−−−− (Equation 1) where τn: current direction reversal period P: number of pole pairs Since the rotation speed is detected in this way, The voltage is applied with the restart frequency f0 as f0 = NP = 1 / (2.tau.n) --- (Equation 2).

Then, during the period D, the steady operating frequency fn is gradually increased. By doing this, when the voltage is reapplied, the inverter output voltage and the residual voltage are in phase,
The starting current is reduced.

The restart frequency f0 can also be calculated as follows. That is, since the number of times the direction of the short-circuit current is reversed in each sampling cycle can be counted and the rotational speed of the induction motor can be calculated by using the count value, the formula 2 can be obtained from f0. N = Pn / (PTS) -------- (Equation 3) where Pn: Number of times of reversal of short circuit current TS: Sampling cycle In the above embodiment, the change in the signal a at the timing Y is detected, and Although the restart was started immediately after that, since the change cycle of the signal a is almost linear when the short cycle is taken, the next cycle is not detected even if the change of the signal a at the timing Y is detected. The change point of can be predicted. That is, as shown in FIG. 5, when the power is restored between t3 and t4, the difference τ3 between the changing times of the signal a at the immediately preceding time t3 and at the preceding time t2 is added to the previous changing time t3. As a result, the next change time t4 can be predicted and calculated. If the time point t4 is set as the restart start point, the same operation can be performed.

According to this embodiment, the zero crossing point of the residual voltage can be detected with high accuracy when applied to the one in which the decrease in the rotation speed is slow.

If the residual voltage disappears, only the applied voltage acts at the time of starting, so that a normal starting method can be used.
This determination can be switched to the normal starting method after the predetermined residual voltage disappearance time has passed. As another method, the determination can be made by the magnitude of the short circuit current i shown in FIG. When the peak value of the short-circuit current detected by the current detector 4 falls below a certain level, the residual voltage disappears and the current level detection circuit 15 shown in FIG.
Then, a signal is issued by the switch to switch to the normal starting method.

In the above description, the signal PB for short-circuiting the upper arm of the inverter is applied, but the lower arm can be similarly implemented.

Further, in the above description, the signal PB is applied during the free-run period, but it may be applied in the same manner if it is applied after the power is restored. However, in this case, the output voltage is 1
The timing of restart is delayed by about a cycle.

[0024]

According to the above invention, since the phase of the residual voltage can be determined by using the existing current detector, it is not necessary to use the conventional phase detector. Therefore, the number of parts is reduced, and it is possible to provide a small-sized, inexpensive and highly reliable inverter.

[Brief description of drawings]

FIG. 1 is a diagram showing a specific example of the present invention.

FIG. 2 is a diagram showing a residual voltage characteristic and a control power supply voltage characteristic of the induction motor during a power failure.

FIG. 3 is a diagram illustrating the operation of a specific example of restarting an instantaneous power failure according to the present invention.

FIG. 4 is a detailed diagram for explaining the operation of a specific example of restarting an instantaneous power failure according to the present invention.

FIG. 5 is an explanatory diagram of another embodiment according to the present invention.

FIG. 6 is a diagram showing a conventional example of an instantaneous power failure restart.

FIG. 7 is a detailed view of a conventional phase detector.

[Explanation of symbols]

1 ... Converter part, 2 ... Smoothing capacitor, 3 ... Inverter part, 4 ... Current detector, 5 ... Induction motor,
6 ... Phase detector, 7 ... Photo coupler, 8 ... Current limiting resistance, 9 ... Power failure detection circuit, 10 ... Inverter control circuit, 11 ... Simultaneous conduction control signal generation command circuit, 12 ...
Current direction reversal detection circuit, 13 ... Restart timing generation circuit, 14 ... Inverter control circuit, 15 ... Current level detection circuit.

Claims (6)

[Claims] 1. A current flowing through an induction motor connected to an output by simultaneously controlling ON / OFF conduction of a switching element of either one of an upper arm and a lower arm of an inverter section after a lapse of a predetermined time from the occurrence of a power failure to a time point when a restart timing is determined. Residual voltage detection means for detecting the frequency and phase of the residual voltage of the induction motor based on the direction, and the residual voltage detection means for determining restart timing based on the residual voltage detection means and the timing at which the power failure is restored. An inverter device comprising means for restarting at the frequency and phase detected by. 2. The residual voltage detecting means simultaneously turns on and off the switching elements of either one of the upper arm and the lower arm with a pulse width of 50% duty or less after a lapse of a predetermined time from the occurrence of a power failure to the time when a restart timing is determined. The inverter device according to claim 1, wherein conduction control is performed. 3. The inverter device according to claim 1, wherein the restart timing is determined by predictive calculation from two current direction reversal times before the timing at which the power failure is restored. 4. A converter unit for converting AC power into DC power, a smoothing capacitor connected to an output of the converter for smoothing the DC power, and a DC power having a switching element and a flywheel diode for an arbitrary frequency. An inverter unit configured to be converted to AC power and supplied to an induction motor connected to an output, a current detection unit that detects an output current of the inverter unit, and a power failure of the input AC voltage of the converter unit. A power failure detection means for detecting, and a simultaneous conduction control means for simultaneously turning on and off a switching element of one of the upper arm and the lower arm of the inverter section while the induction motor is free running based on the output of the power failure detecting means. And a current direction detection that detects the direction in which the output current of the inverter section flows based on the output of the current detector. A step, a frequency detection means for detecting the frequency of the residual voltage of the induction motor in operation of the simultaneous conduction control means based on the current direction detection means, an output of the power failure detection means and an output of the current direction detection means A restart timing generating means for outputting a restart command based on the output, a phase detecting means for detecting a phase of the residual voltage based on the restart command and the output of the current direction detecting means, an output of the frequency detecting means and the An inverter device comprising means for restarting at a frequency and a phase based on the output of the phase detecting means. 5. A first step of simultaneously controlling ON / OFF conduction of switching elements of either one of the upper and lower arms of the inverter section after a lapse of a predetermined time after the occurrence of power failure, and an output connected during the first step. The second step of detecting the frequency of the residual voltage of the induction motor, the third step of detecting the direction reversal of the output current after the power failure is restored, and the case where the direction reversal of the output current is detected in the third step. A fourth step of stopping the first step, a frequency corresponding to the frequency detected in the second step and the direction of the output current detected in the third step in response to the stop of the first step, A method for restarting a momentary power failure of an inverter device, comprising a fifth step of applying a voltage having a phase and voltage value to an induction motor connected to the output and restarting. 6. The direction reversal timing of the output current in the third step is detected by predictive calculation from two current direction reversal timings before the timing at which the power failure is restored. Method for restarting an instantaneous power failure of an inverter device.